Fabrication and Reliability Study of Wide Band Polymer Matrix Composite Radomes

Abstract

Fiber reinforced composites are utilized for conventional to advanced applications including energy storage, aerospace, and microelectronics. Polymer matrices embedded with glass fibers are used in making protective enclosure “radome”, which works as an interface between the communication antennas and environment. In this role, Silica fiber reinforced/Epoxy (SFE or SiO2/E) composites offer minimum interference in signal transmission owing to their intrinsic low dielectric properties, good mechanical strength, and durability in external environmental conditions. SiO2/E composite was fabricated from a cost-effective high-silica fibers impregnated in epoxy resin (30%, 40%, 50%, 60%, 70%, 80% and 90% wt. of fibers) by hand lay-up and compression molding. SFE composite with 80% fiber loading was found with reasonable combination of properties, where its dielectric constant (Ɛr= 3.17) and dielectric loss (δ= 0.036) determined by network analyzer. The mechanical properties measured on Universal Testing Machine (UTM) where tensile strength was observed 155.7 MPa, compressive strength was 409.64 MPa, and flexural strength was 311.9 MPa. Scanning Electron Microscope (SEM) showed the SFE composite morphology, fair fiber-matrix adhesion, interface, and cracks initiation upon aging. The Fourier Transformation InfraRed (FTIR) spectra showed epoxide, Hydroxyl linkage, Si-O and organic functional groups. Dynamic mechanical analyzer determined the storage modulus, loss modulus, damping factors of Silica Fiber/Epoxy composite. Progressive degradation of SFE composite radome performance and material properties upon prolonged environmental exposure were evaluated. Upon real time aging (four-years) the Ɛr was gradually raised from 3.2 to 4.49 (40%) and δ from 0.035 to 0.045 (28.2 %). Upon accelerated environmental conditions (using Hallberg Peck model), the SFE composite Ɛr was increased from 3.2 to 4.53 and δ from 0.035 to 0.071 along with lowering of fiber-matrix adhesion, while the long-term performance of SFE compositePatch antenna radome, antenna gain was decreased from 7.65 dB to 7.5 dB. The simulated reliability of SFE composite material reached 20 % after 12 years. During a 30 days hygrothermal aging of Silica Fiber/Epoxy composite at 5 °C,50 °C,70 °C and 80 °C, the Ɛr was reached from 3.21 to 3.26, δ raised from 0.045 to 0.051 and moisture absorption was xix found with 1.83 %. In hygrothermally aged SiO2/E composite the thermal expansion coefficient(α) was varied from 5.79 x10-6 K -1 to 5.89 x10-6 K -1 and its thermal conductivity (k) was slightly increased from 0.395 to 0.401 Wm-1K -1 than unaged SiO2/E composite. The reasonable retention of dielectric, mechanical, thermal properties, low moisture uptake in different environmental exposures, referred to the suitability of SiO2/E composite in low dielectric constant applications. Furthermore, the SiO2/E composite radome performance coupled with patch antenna was found reliable upon real time environmental aging.